1. Field of the Invention
The present invention relates generally to a signal processing stage useful in laser projection systems, television systems, and the like. In particular, this invention relates to an electronics circuit which separates the horizontal sync signal, the vertical sync signal and the video information signal from an incoming composite video signal.
2. Description of the Prior Art
Heretofore, numerous electronic circuits have been employed for separating horizontal and vertical sync signals from an incoming composite video signal. Such systems are too numerous to discuss herewith. Besides, most thereof constitute prior art devices which are well known to the artisan, thereby obviating the need for further discussion thereof.
Of course, there are several prior art devices which are of some significance, inasmuch as they at least remotely or indirectly concern subject matter that is pertinent to the system constituting the instant composite video signal separator.
For example, U.S. Pat. No. 3,532,811 to Bert H. Dann discloses a circuit for separating sync signals from a composite video signal, the operation of which is based on the fact that the time the video signal is at sync tip level during one field is fixed in relation to the total time of one field in a standardized television broadcast signal. A capacitor is arranged to be charged from a first current source and discharged by a second current source, the current sources having essentially constant current and the currents being in the same ratio as the ratio of the time the video signal is not at sync tip level to the time the voltage is at sync tip level. The voltage across the capacitor controls the turning on and turning off of an output transistor in synchronism with the sync tips of the composite video input signal.
U.S. Pat. No. 3,743,774 to Jack R. Chipman and Joseph E. Morrow discloses a synchronizing signal separational circuit which has an improved active low pass filter for passing only vertical synchronizing signals, a passive high pass filter for passing horizontal synchronizing signals, and an amplifier which supplies both vertical and horizontal synchronizing signals to the filters after clipping and limiting a detected video signal to eliminate video information signals and noise, respectively.
U.S. Pat. No. 3,736,378 to Peter E. Haferl discloses a video signal processing stage for a television receiver which performs the combined functions of video demodulation, automatic gain control voltage generation, horizontal synchronizing pulse separation, and vertical synchronizing pulse separation in a signal circuit.
While satisfactory for their intended purposes, that of horizontal and vertical sync signal separation, the first two mentioned devices of the prior art fail to separate video information from an incoming composite video signal. With respect to the last mentioned device of the prior art, it is complex in design, does not perform exactly the same functions as the subject invention, and contains a combination of elements that is somewhat different from that of the present invention.